A stent is typically a hollow, generally cylindrical device that is deployed in a body lumen from a radially contracted configuration into a radially expanded configuration, which allows it to contact and support a vessel wall. A plastically deformable stent can be implanted during an angioplasty procedure by using a delivery system that includes a balloon catheter bearing a compressed or “crimped” stent, which has been loaded onto the balloon. The stent radially expands as the balloon is inflated, forcing the stent into contact with the body lumen, thereby forming a support for the vessel wall. Deployment is effected after the stent has been introduced percutaneously, transported transluminally, and positioned at a desired location by means of the balloon catheter. Similarly, a self-expanding stent is formed from a memory shape material that tends to return to its radially expanded configuration. The stent is crimped into a radially compressed configuration within a sleeve of a delivery catheter. After delivery to the treatment site, the sleeve is withdrawn such that the stent is permitted to expand to its radially expanded configuration.
Stents may be formed from wire(s), may be cut from a tube, or may be cut from a sheet of material and then rolled into a tube-like structure. Stents cut from a tube or from a sheet of material normally are oriented substantially perpendicular to a longitudinal axis of the stent. Similarly, some stents formed from wires have the wires formed into a plurality of rings that are aligned parallel to each other and connected to each, and are also oriented substantially perpendicular to the longitudinal axis of the stent. Helically wound stents may be formed by helically wrapping a wire around a mandrel with pins disposed thereon. The pattern of the pins on the mandrel determines the shape of the tubular waveform formed. Helically wound stents, such as those described in U.S. Pat. No. 4,886,062 to Wiktor, the contents of which are incorporated herein by reference, may also be formed by forming a wire into a waveform, such as a sinusoid, that is then helically wrapped around a mandrel to provide a tubular or cylindrical structure. Helically wound stents, however, generally include ends that are not substantially perpendicular to the longitudinal axis of the stent. In other words, due to the helical winding of the waveform, a portion of each end of the stent extends further longitudinally than the remainder of each end of the stent, as shown in FIG. 2 of the Wiktor patent.
In some helically wound stents, such as those described in U.S. Pat. No. 5,314,472 to Fontaine, end portions of the wire have a reduced amplitude waveform as compared to the waveforms in the middle of the wire. Wrapping such a wire around a mandrel to form a stent may result in a stent with ends that may be generally perpendicular to the longitudinal axis of the stent.
However, these types of stents with end segments with a different waveform than the central segment of the stent may be inefficient to manufacture. For example, if a single wire is used, the waveform must be changed at least once (normally twice as each end segment normally has the waveform variation). For example, the waveform for a first end segment is started on the wire, then the waveform is changed to the waveform for the central segment, then the waveform must again be changed for the second end segment. Further, the waveforms for each stent must essentially be individually made, either by using only a length of wire for the stent, or by creating several waveforms in a wire in the order necessary to make each individual stent. In other methods, the end segments are made separate from the central segment and attached thereto. However, using these methods, the ends of the central segment and ends segments may be raw ends that could potentially damage the vessel into which the stent is to be implanted, or parts of the catheter used to deliver the stent.
Accordingly, it would be desirable to be able to create the waveform for the central segment of the stent in bulk. Similarly, it would be desirable to make the waveform for the end segments in bulk. Then, when it is desired to make a stent of a given length, the bulk central waveform can be cut to the appropriate length, and joined to the end segment waveforms in a manner that provides ends that are substantially orthogonal to the longitudinal axis of the stent and without exposed raw ends of the wires.